MOSCOW (Reuters) - Google removed a YouTube advert by Russian opposition leader Alexei Navalny after authorities complained that the videos would violate an election silence law before Sunday’s vote for regional governors, an aide to Navalny said on Saturday.

The series of YouTube videos featured Navalny inviting Russians to join demonstrations on Sunday, when polls suggest President Vladimir Putin’s former chief-of-staff Sergei Sobyanin will be comfortably re-elected as the capital’s mayor.

Navalny’s aide, Leonid Volkov, said in a social media post that Google deleted the videos after the Central Election Commission had sent a letter of complaint to Google about the advertisement — a demand Volkov called illegal.

Google’s Russian office said in an emailed comment: “We consider all justified appeals from state bodies. We also require advertisers to act in accordance with the local law and our advertising policies.”

Navalny, who ran against Sobyanin in 2013 and had planned to lead a protest against proposed pension changes on Sunday, will spend election day behind bars after being convicted of violating protest laws. His supporters plan to demonstrate across Russia.

While Sobyanin appears on track for an easy win, public anger over the planned increases to the nationwide pension age means many voters may stay away, which would tarnish his victory, some political analysts have said.

Elections will also be held for the governorships of another 25 of Russia’s 85 regions.